Lorry-based concrete mixers are supplied with a movable discharge chute which can be positioned in various configurations to allow the discharge of concrete from the mixer drum.
After discharge of concrete, it is extremely desirable to wash down the chute as quickly as possible to remove concrete residue. If this residue is not removed relatively quickly, it can set on the chute, adhering to the chute surface and creating a build up of concrete.
This build up residue can have a number of negative effects. For example if the residue breaks free of the surface whilst the vehicle is in transit there is a high risk of the residue hitting a vehicle travelling behind the concrete mixer.
Furthermore, the residue build up increases the weight of the truck and particularly the discharge chute, putting undue strain on the chute support structure.
However, it is not always possible to clean the chute immediately after discharge as a growing number of construction companies are restricting or even banning lorry-based concrete mixers from washing down chutes on site to ensure site compliance with environmental regulations such as the Water Resources Act 1991, the Water Industry Act 1991, the Anti Pollution Works Regulations 1999, and the Environmental Permitting Regulations (EPR) 2010.
Additionally there is a problem with stones in the drum bouncing out of the drum and down the chute when the mixer is in transit, posing a similar danger as the residue to other vehicles.
These problems have been alleviated by supplying a lorry based mixer with a method of collecting and storing the chute wash water and loose stones and debris in a tank until such times as the contaminated water can be disposed of correctly. However, it has been found that a layer of sludge can build up in these tanks and the tanks can, subsequently, be difficult to empty.